1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for data transmission in a multiple-carrier system.
2. Related Art
The institute of electrical and electronics engineers (IEEE) 802.16e standard was adopted in 2007 as a sixth standard for international mobile telecommunication (IMT)-2000 in the name of ‘WMAN-OFDMA TDD’ by the ITU-radio communication sector (ITU-R) which is one of sectors of the international telecommunication union (ITU). An IMT-advanced system has been prepared by the ITU-R as a next generation (i.e., 4th generation) mobile communication standard following the IMT-2000. It was determined by the IEEE 802.16 working group (WG) to conduct the 802.16m project for the purpose of creating an amendment standard of the existing IEEE 802.16e as a standard for the IMT-advanced system. As can be seen in the purpose above, the 802.16m standard has two aspects, that is, continuity from the past (i.e., the amendment of the existing 802.16e standard) and continuity to the future (i.e., the standard for the next generation IMT-advanced system). Therefore, the 802.16m standard needs to satisfy all requirements for the IMT-advanced system while maintaining compatibility with a mobile WiMAX system conforming to the 802.16e standard.
Effective transmission/reception methods and utilizations have been proposed for a broadband wireless communication system to maximize efficiency of radio resources. An orthogonal frequency division multiplexing (OFDM) system capable of reducing inter-symbol interference (ISI) with a low complexity is taken into consideration as one of next generation wireless communication systems. In the OFDM, a serially input data symbol is converted into N parallel data symbols, and is then transmitted by being carried on each of separated N subcarriers. The subcarriers maintain orthogonality in a frequency dimension. Each orthogonal channel experiences mutually independent frequency selective fading, and an interval of a transmitted symbol is increased, thereby minimizing inter-symbol interference.
When a system uses the OFDM as a modulation scheme, orthogonal frequency division multiple access (OFDMA) is a multiple access scheme in which multiple access is achieved by independently providing some of available subcarriers to a plurality of users. In the OFDMA, frequency resources (i.e., subcarriers) are provided to the respective users, and the respective frequency resources do not overlap with one another in general since they are independently provided to the plurality of users. Consequently, the frequency resources are allocated to the respective users in a mutually exclusive manner. In an OFDMA system, frequency diversity for multiple users can be obtained by using frequency selective scheduling, and subcarriers can be allocated variously according to a permutation rule for the subcarriers. In addition, a spatial multiplexing scheme using multiple antennas can be used to increase efficiency of a spatial domain.
Meanwhile, a radio resource can be divided into a plurality of frequency partitions (FPs) when providing services such as multicast and broadcast services (MBS). This is called fractional frequency reuse (FFR). Each FP can be used for a different usage. In each FP, a distributed subchannel and a localized subchannel may coexist in a frequency division multiplexing (FDM) manner. In addition, each FP can configure a subchannel on the basis of a different-sized resource granularity. When the subchannel is configured, there is a need to consider various factors and a trade-off based on the various factors.
In addition, an IEEE 802.16m system may consider not only a single carrier but also multiple carriers. According to a user equipment, only one carrier may be accessed or several carriers may be accessed. When supporting multiple carriers, a guard subcarrier may be allocated to decrease interference between carriers. However, for effective resource utilization, there is a need to use the guard subcarrier in data transmission.
Accordingly, there is a need for effective subchannelization considering a guard subcarrier when supporting multiple carriers.